1. Field of the Invention
The present invention relates to a power transfer device for four-wheel drive vehicles, and more particularly to a shift mechanism in the power transfer device.
2. Description of the Prior Art
In Japanese Patent Early Publication No. 61-207219, there has been proposed a power transfer device for four-wheel drive adapted for use in combination with a primary power transmission of an automotive vehicle. The power transfer device includes a housing, a first shaft rotatably mounted within the housing and having an input end for drive connection to an output shaft of the power transmission and an output end for drive connection to a set of rear-wheel or front-wheel drive axles, a second shaft rotatably mounted within the housing in parallel with the first shaft and having an output end for drive connection to a set of front-wheel or rear-wheel drive axles, and a shift mechanism including a pair of clutch sleeves each mounted on the first and second shafts and shiftable between respective positions in which they effect drive connection or disconnection between the first and second shafts, a shift rod arranged in parallel with the first and second shafts and axially movably mounted within the housing, and a shift fork mounted on the shift rod for axial movement therewith and coupled with the clutch sleeves for shifting them in response to the axial movement of the shift rod.
In the case that an ancillary change-speed mechanism, a limited-slip differential and the like are mounted on the first shaft, shifting amounts of the clutch sleeves are restricted respectively in a different distance. In a condition where one of the clutch sleeves is arranged to be axially shifted in a small distance while the other clutch sleeve to be axially shifted in a large distance, the shift fork does not act to shift the latter clutch sleeve to its stroke end. To avoid such a problem, the single shift fork may be replaced with two shift forks which are mounted on two parallel shift rods and coupled with the clutch sleeves, respectively. In such an arrangement, however, a shift mechanism for the two shift rods becomes complicated in construction and large in size.